15 x 8.5 rally wheels?

[grebus1]

I'm considering buying some used original truck rallys for my '72 Burb. The seller says they are 15" x 8.5", but the only factory ones I've seen on our trucks have been 7" or 8". I tried to search the boards for some help, but that only seems to confuse me more!

Will these fit OK on my truck or will they be too wide? Also, is the back spacing and lug pattern the same on all factory rallys or should I be looking for a specific size? I have a couple pics if that might help. Thanks in advance...